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2 Acta Physiologiae Plantarum

2 2013

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How do expansins control plant growth? A model for cell wall loosening via defect migration in cellulose microfibrils

100%

Lipchinsky A.

nr 12

Expansins are plant cell wall-loosening proteins that promote cell growth and are essential for many critical developmental processes and stress responses. The molecular basis for expansin action is uncertain. Recently, it has been proposed that expansins loosen the wall by means of the generation of mobile conformational defects at the surface of cellulose microfibrils. The present work addresses this hypothesis by elaborating three assumptions: (1) microfibril–matrix interfaces cause steep stress gradients on the microfibril surface, (2) stress gradients drive the motion of conformational defects along the microfibril surface toward the microfibril–matrix interfaces, and (3) the approach of the defects to the microfibril–matrix interfaces facilitates the dissociation of matrix polysaccharides from cellulose microfibrils.

Elastic properties of the growth-controlling outer cell walls of maize coleoptile epidermis

51%

Lipchinsky A. , Sharova E. I. , Medvedev S. S.

2013

tom 35

nr 07

The effects of tensile stress and temperature on cell wall elasticity have been investigated in the outer cell walls of coleoptile epidermis of 4- and 6-day-old Zea mays L. seedlings. The change in tensile stress from 6 to 40 MPa caused the increase in cell wall elastic modulus from 0.4 to 3 GPa. Lowering the temperature from 30 to 4 ºC resulted in instantaneous and reversible cell wall elongation of 0.3–0.5 %. At a given temperature and stress level, the wall elastic modulus of 6-day-old seedlings tended to be 30 % higher than that of 4-day-old plants. The relationship between cell wall elasticity and mechanical stress indicated that the stress distribution within the cell wall is highly uneven. The analysis of the effect of temperature on cell wall elastic strain showed that structural differences between crystalline and amorphous load-bearing polymers were not the only cause of the uneven stress distribution. Based on the results obtained by Hejnowicz and Borowska- Wykręt (Planta 220:465–473, 2005), we suggested that the uneven stress distribution is partially related to the stress gradient between inner and outer layers of the cell wall.